arXiv subjects

Y. Q. Pan

Publications and source records attributed to Y. Q. Pan.

3 recordsLinked to original sources

arXiv2024

Intrinsic pinning of FeSe$_1$$_-$$_x$S$_x$ single crystals probed by torque magnetometry

Intrinsic pinning is caused by natural pinning centers that occur because of the modulation of the order parameter or weak superconducting layers. Early work has shown that intrinsic pinning generates a high pinning force and critical current density in some layered oxide superconductors. Studying the intrinsic pinning of superconductors is crucial for both fundamental studies and potential applications. Herein, we use torque magnetometry to study angle-resolved in-plane and out-of-plane magnetic torque for a series of high-quality FeSe$_1$$_-$$_x$S$_x$ single crystals. A fourfold torque signal was observed when the magnetic field was within the \textit{ab} plane. We interpret that this fourfold in-plane irreversible torque is from the intrinsic pinning due to combined effects of gap nodes/minimum and twin domains. Additionally, we attributed the observed out-of-plane torque peaks to intrinsic pinning due to the layered structure.

cond-mat.supr-con↗

arXiv2024

Multiple magnetic orders discovered in the superconducting state of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$

The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe$_{2}$As$_{2}$-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe$_{2}$As$_{2}$-based crystal, which were deemed to originate from the itinerant Fe moments ($\sim$ 190 K) and the localized Eu$^{2+}$ moments ($\sim$ 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ crystals with \textit{x} = 0.21 (optimally doped) and \textit{x} = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ have detected the new low-temperature magnetic orders, which may originate from the localized Eu$^{2+}$ spins order or the spin reorientation.

cond-mat.supr-con↗

arXiv2021

Disorder-robust high-field superconducting phase of FeSe single crystals

When exposed to high magnetic fields, certain materials manifest an exotic superconducting (SC) phase that has attracted considerable attention. A proposed explanation for the origin of the high-field SC phase is the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. This state is characterized by inhomogeneous superconductivity, where the Cooper pairs have finite center-of-mass momenta. Recently, the high-field SC phase was observed in FeSe, and it was deemed to originate from the FFLO state. Here, we synthesize FeSe single crystals with different levels of disorder. The level of disorder is expressed by the ratio of the mean free path to the coherence length and ranges between 35 and 1.2. The upper critical field \textit{B}$_{\rm{c}2}$ was obtained by both resistivity and magnetic torque measurements over a wide range of temperatures, which went as low as $\sim$0.5 K, and magnetic fields, which went up to $\sim$38 T along the \textit{c} axis and in the \textit{ab} plane. In the high-field region parallel to the \textit{ab} plane, an unusual SC phase was confirmed in all the crystals, and the phase was found to be robust against disorder. This result suggests that the high-field SC phase in FeSe is not a conventional FFLO state.

cond-mat.supr-con↗